03-17-2011, 01:17 PM
Tony Williams Wrote:Gene, I don't think it necessarily follows that a military ball round can't have a high BC. Someone on my own forum (who knows a lot more about the technicalities of bullet design than I do) pointed about that the German 7.92mm heavy ball of WW2 was superbly shaped, with a ballistic coefficient of over .5, yet was churned out by the billion. So while I agree that no military is going to be selecting a match-grade bullet, a ball round which matched the shape and weight of such a bullet shouldn't be far behind.
As it is, the Grendel's 123 grain Scenar overtakes 7.62mm ball in retained energy by about 700 metres and by 1000 metres is clearly ahead, with a flatter trajectory and less wind drift too. Given that what is needed to replace 7.62mm is to match M80 performance at long range, there can afford to be some loss of Grendel performance while still achieving this.
Bullet design is the crucial issue in the success of a long-range intermediate. It has to have low drag, but also yaw rapidly and reliably on impact in order to provide effectiveness against unprotected personnel. If the bullet also has to be lead-free that brings further design headaches...
As far as barrel length is concerned, a general-purpose cartridge really should be used in a general-purpose rifle to get the most out of it. That means the barrel should be long enough to get the most out of the cartridge. Since a general-purpose rifle also needs to be compact for urban fighting, that strongly indicates the bullpup configuration as the optimum solution (although I know most Americans don't agree!). I've considered the pros and cons of bullpups, and ways of tackling their issues, HERE.
Tony:
I would have to look at that round of 8mm but shape doesn't always mean performance. I am pretty sure (since I pulled and sectioned some) that the later British .303 had a bullet that put wood filler into the tip to enhance yaw when it hit something. Long shape allows for more streamlined design -- thus a higher BC. The problem it that this is seen only through equations written on a piece of paper. Its exterior performance sucked.
I keep hearing about the exterior performance of this 123 Lapua Grendel load and how it overcomes M-80 so decided to test it. KD range to 1000 yards, sea level, air temperature was around 55 if I recall. Very experienced guys working the targets in the pits. 24 and 26" barrel match grade Grendels with the 123 Lapua, 30.5 grains of 2520 (the fastest load I have found to date that theoretically stays inside safe limits), Grendel brass, CCI-450 primer.
The guy pulling targets could barely hear the bullet at 1000 yards from either barrel length. I expect it went subsonic at around 700 or 800 yards, just like M-80, which actually is pretty much what I expected. So, what happens via a ballistic computer doesn't always happen in reality. And in practical terms, considering the full environment of use, does it really matter? BTW -- we threw some 118 LR and SB through a couple of Remingtons and that ammo did stay above the speed of sound.
This discussion went on for years on the old forum and was actually pretty neat to read. It changed its title a hundred times when things got off track but they always went off track no matter what. Maybe we should have paid more attention to their direction when they did go off track as that was probably the more realistic assessment.
LR1955